Muscles require a large amount of energy to function. This is provided primarily by mitochondria in cells that consume a lot of energy. We therefore find more of these powerhouses of the cell in muscle cells than in other cell types with a lower metabolic rate.
Muscle cells are assiciated with a large number of mitochondria as they require more ATP (energy) to function than other cells. They need this because of their frequent contraction and relaxation, which requires more ATP than average cells.
Sexual reproduction is a type of life cycle where generations alternate between cells with a single set of chromosomes (haploid) and cells with a double set of chromosomes.Sexual reproduction is by far the most common life cycle in eukaryotes, for example animals and plants.
The sympathetic nervous system is activated when you are surprised. When you are surprised that sympathetic nervous system send neural impulses to the adrenal glands (just above the kidneys) to release stress hormones (adrenaline and norepinephrine) and send it to your bloodstream. That why when you are surprised your heart, beats too fast and you sweat too much.